SWITCHER AT THE TIME OF ABNORMAL SYNCHRONOUS POSITION SIGNAL OF LINEAR MOTOR

PURPOSE:To detect occurrence of abnormality and to make automatic switching to other system by employing a second synchronous position detection signal and compar ing the phase of a first reference synchronous position signal with that of a stabilized synchronous signal. CONSTITUTION:A second synchronous position signal 5 is produced from other cross induction line system or speed electromotive force in order to detect abnormal reference synchronous signals 1, 2, and a phase difference comparing section 6 detects phase differences between three signals. A sine wave at a stabilizing section 2 is normally selected through a switching section 3 which then produces a synchronous position signal 4, i.e., a sins wave for operating a linear motor. The stabilizing section 2 produces an abnormal output when the phase difference between the output from the stabilizing section 2 and the first synchronous position signal 1 and the phase difference between the output from the stabilizing section 2 and the second synchronous position signal 5 exceed a predetermined level. If the phase difference between the first and second synchronous position signals 1, 5 is normal at that time, a switching section 3 is switched to upper side to employ the first synchronous position signal.